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    <title>Document</title>
    <script>
        /*  从以下学员名单中随机选出4个学员：
         var arr = ["鹿晗", "王俊凯", "蔡徐坤", "彭于晏", "周杰伦", "刘德华", "赵本山"]；
             注意：不要有重复的学员 */


        //获取一个随机数
        function countDown(min, max) {
            return Math.floor(Math.random() * (max - min + 1)) + min
        }
        
        var arr = ["鹿晗", "王俊凯", "蔡徐坤", "彭于晏", "周杰伦", "刘德华", "赵本山"]
        var newArr = []
        for(var i = 1; ; i++) {
            var index = countDown(0, (arr.length - 1))
            if(newArr.indexOf(arr[index]) == -1) {
                newArr.push(arr[index])
            }  
            if(newArr.length == 4) {
                break
            }
        }
        console.log(newArr);
    </script>
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